In transmission systems with high bit rates, the decision threshold (sampling threshold) and the sampling instant of a transmitted signal substantially determines the error rate and, hence, the maximum transmission range. The optimum decision threshold, that is to say the threshold for distinguishing between the two states of the binary signal, and the optimum sampling instant, that is to say the phase angle of a sampling clock signal relative to the bit center of a data signal, are dependent on the transmission device and the transmission link. During operation, both are intended to be readjusted without interfering with the transmission.
The published German patent application DE 191 77 643 A1 describes a method and an arrangement for regulating the decision threshold and the sampling instant of a data regenerator. The latter has a first data path with a phase comparator and a second data path, the decision thresholds in the two data paths being able to be set independently of one another. As a result of this, the decision threshold can be optimized at a predetermined sampling instant. In order to determine the entire reception eye, however, the sampling instant has to be shifted. This is only possible jointly for both data paths, as a result of which the reception quality is impaired in the event of relatively large deviations from the ideal sampling instant. Moreover, the reference with respect to the ideal phase angle is easily lost in the event of relatively large phase deviations and non-ideal transmission conditions.
The published German patent application DE 197 17 642 A1 describes a data regenerator having only one data path with an adjustable decision threshold and an adjustable sampling instant. The phase comparator is independent of the setting of the sampling instant. This data regenerator is preferably used in systems which transmit data protected by error-correcting codes, as a result of which the impairment of the signal quality, through alteration of the sampling conditions, is eliminated or alleviated by the error correction. However, this arrangement is not suitable for the measurement of the entire reception eye and in the case of transparent transmission.
In the case of optimization of the sampling, it must be taken into account, moreover, that the decision threshold and the sampling instant influence one another.
It is an object of the present invention, therefore, to specify data regenerators for transparent transmission systems in which the decision threshold and the sampling instant can be set optimally.